Marinobacter qingdaonensis sp. nov., a moderately halotolerant bacterium isolated from intertidal sediment.

A Gram-stain-negative, aerobic, rod-shaped and halotolerant bacterium, designated as strain ASW11-75T, was isolated from intertidal sediments in Qingdao, PR China, and identified using a polyphasic taxonomic approach. Growth of strain ASW11-75T occurred at 10-45 °C (optimum, 37 °C), pH 6.5-9.0 (optimum, pH 8.0) and 0.5-18.0 % NaCl concentrations (optimum, 2.5 %). Phylogenetic analyses based on 16S rRNA gene sequences and 1179 single-copy orthologous clusters indicated that strain ASW11-75T is affiliated with the genus Marinobacter. Strain ASW11-75T showed highest 16S rRNA gene sequence similarity to 'Marinobacter arenosus' CAU 1620T (98.5 %). The digital DNA-DNA hybridization and average nucleotide identity values between strain ASW11-75T and its closely related strains (Marinobacter salarius R9SW1T, Marinobacter similis A3d10T, 'Marinobacter arenosus' CAU 1620T, Marinobacter sediminum R65T, Marinobacter salinus Hb8T, Marinobacter alexandrii LZ-8T and Marinobacter nauticus ATCC 49840T) were 19.8-24.5 % and 76.6-80.7 %, respectively. The predominant cellular fatty acids were C16 : 0, C18 : 1 ω9c and C16 : 0 N alcohol. The polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified aminophospholipid and two unidentified lipids. The major isoprenoid quinone was ubiquinone-9. The genomic DNA G+C content was 62.2 mol%. Based on genomic and gene function analysis, strain ASW11-75T had lower protein isoelectric points with higher ratios of acidic residues to basic residues and possessed genes related to ion transport and organic osmoprotectant uptake, implying its potential tolerance to salt. The results of polyphasic characterization indicated strain ASW11-75T represents a novel Marinobacter species, for which the name Marinobacter qingdaonensis sp. nov. with the type strain ASW11-75T is proposed. The type strain is ASW11-75T (=KCTC 82497T=MCCC 1K05587T).

Gradients of bacteria in the oceanic water column reveal finely-resolved vertical distributions.

Bacterial communities directly influence ecological processes in the ocean, and depth has a major influence due to the changeover in primary energy sources between the sunlit photic zone and dark ocean. Here, we examine the abundance and diversity of bacteria in Monterey Bay depth profiles collected from the surface to just above the sediments (e.g., 2000 m). Bacterial abundance in these Pacific Ocean samples decreased by >1 order of magnitude, from 1.22 ±0.69 ×106 cells ml-1 in the variable photic zone to 1.44 ± 0.25 ×105 and 6.71 ± 1.23 ×104 cells ml-1 in the mesopelagic and bathypelagic, respectively. V1-V2 16S rRNA gene profiling showed diversity increased sharply between the photic and mesopelagic zones. Weighted Gene Correlation Network Analysis clustered co-occurring bacterial amplicon sequence variants (ASVs) into seven subnetwork modules, of which five strongly correlated with depth-related factors. Within surface-associated modules there was a clear distinction between a 'copiotrophic' module, correlating with chlorophyll and dominated by e.g., Flavobacteriales and Rhodobacteraceae, and an 'oligotrophic' module dominated by diverse Oceanospirillales (such as uncultured JL-ETNP-Y6, SAR86) and Pelagibacterales. Phylogenetic reconstructions of Pelagibacterales and SAR324 using full-length 16S rRNA gene data revealed several additional subclades, expanding known microdiversity within these abundant lineages, including new Pelagibacterales subclades Ia.B, Id, and IIc, which comprised 4-10% of amplicons depending on the subclade and depth zone. SAR324 and Oceanospirillales dominated in the mesopelagic, with SAR324 clade II exhibiting its highest relative abundances (17±4%) in the lower mesopelagic (300-750 m). The two newly-identified SAR324 clades showed highest relative abundances in the photic zone (clade III), while clade IV was extremely low in relative abundance, but present across dark ocean depths. Hierarchical clustering placed microbial communities from 900 m samples with those from the bathypelagic, where Marinimicrobia was distinctively relatively abundant. The patterns resolved herein, through high resolution and statistical replication, establish baselines for marine bacterial abundance and taxonomic distributions across the Monterey Bay water column, against which future change can be assessed.

Nitrogen-fixing organelle in a marine alga.

Symbiotic interactions were key to the evolution of chloroplast and mitochondria organelles, which mediate carbon and energy metabolism in eukaryotes. Biological nitrogen fixation, the reduction of abundant atmospheric nitrogen gas (N2) to biologically available ammonia, is a key metabolic process performed exclusively by prokaryotes. Candidatus Atelocyanobacterium thalassa, or UCYN-A, is a metabolically streamlined N2-fixing cyanobacterium previously reported to be an endosymbiont of a marine unicellular alga. Here we show that UCYN-A has been tightly integrated into algal cell architecture and organellar division and that it imports proteins encoded by the algal genome. These are characteristics of organelles and show that UCYN-A has evolved beyond endosymbiosis and functions as an early evolutionary stage N2-fixing organelle, or "nitroplast."

Impact of airborne algicidal bacteria on marine phytoplankton blooms.

Ocean microbes are involved in global processes such as nutrient and carbon cycling. Recent studies indicated diverse modes of algal-bacterial interactions, including mutualism and pathogenicity, which have a substantial impact on ecology and oceanic carbon sequestration, and hence, on climate. However, the airborne dispersal and pathogenicity of bacteria in the marine ecosystem remained elusive. Here, we isolated an airborne algicidal bacterium, Roseovarius nubinhibens, emitted to the atmosphere as primary marine aerosol (referred also as sea spray aerosols) and collected above a coccolithophore bloom in the North Atlantic Ocean. The aerosolized bacteria retained infective properties and induced lysis of Gephyrocapsa huxleyi cultures.This suggests that the transport of marine bacteria through the atmosphere can effectively spread infection agents over vast oceanic regions, highlighting its significance in regulating the cell fate in algal blooms.

Complete genome sequence of the novel Antarctic Oceanisphaera sp. IT1-181 that carried five plasmids.

Bacteria of the genus Oceanisphaera in the class Gammaproteobacteria are widely distributed in marine environments. Oceanisphaera sp. IT1-181 was isolated from intertidal sediment in the coastal region of the Chinese Great Wall Station on the Fildes Peninsula, King George Island, Antarctica. Here, we sequenced the complete genome of strain IT1-181, which contained a single chromosome of 3,572,184 bp (G + C content of 49.89 mol%) with five plasmids. A total of 3229 protein-coding genes, 88 tRNA genes, and 25 rRNA genes were obtained. Genome sequence analysis revealed that strain IT1-181 was not only a potentially novel species of the genus Oceanisphaera, but also harbored genes involved in biosynthesizing ectoine as well as poly-ß-hydroxybutyric acid (PHB). In addition, genes of a complete type I-E CRISPR-Cas system were found in the bacterium. The results indicate the potential of strain Oceanisphaera sp. IT1-181 in biotechnology and are helpful for us understanding its ecological roles in the changing Antarctic intertidal zone environment.

Disentangling top-down drivers of mortality underlying diel population dynamics of Prochlorococcus in the North Pacific Subtropical Gyre.

Photosynthesis fuels primary production at the base of marine food webs. Yet, in many surface ocean ecosystems, diel-driven primary production is tightly coupled to daily loss. This tight coupling raises the question: which top-down drivers predominate in maintaining persistently stable picocyanobacterial populations over longer time scales? Motivated by high-frequency surface water measurements taken in the North Pacific Subtropical Gyre (NPSG), we developed multitrophic models to investigate bottom-up and top-down mechanisms underlying the balanced control of Prochlorococcus populations. We find that incorporating photosynthetic growth with viral- and predator-induced mortality is sufficient to recapitulate daily oscillations of Prochlorococcus abundances with baseline community abundances. In doing so, we infer that grazers in this environment function as the predominant top-down factor despite high standing viral particle densities. The model-data fits also reveal the ecological relevance of light-dependent viral traits and non-canonical factors to cellular loss. Finally, we leverage sensitivity analyses to demonstrate how variation in life history traits across distinct oceanic contexts, including variation in viral adsorption and grazer clearance rates, can transform the quantitative and even qualitative importance of top-down controls in shaping Prochlorococcus population dynamics.

Growth and mortality of aerobic anoxygenic phototrophs in the North Pacific Subtropical Gyre.

Aerobic anoxygenic phototrophic (AAP) bacteria harvest light energy using bacteriochlorophyll-containing reaction centers to supplement their mostly heterotrophic metabolism. While their abundance and growth have been intensively studied in coastal environments, much less is known about their activity in oligotrophic open ocean regions. Therefore, we combined in situ sampling in the North Pacific Subtropical Gyre, north of O'ahu island, Hawaii, with two manipulation experiments. Infra-red epifluorescence microscopy documented that AAP bacteria represented approximately 2% of total bacteria in the euphotic zone with the maximum abundance in the upper 50 m. They conducted active photosynthetic electron transport with maximum rates up to 50 electrons per reaction center per second. The in situ decline of bacteriochlorophyll concentration over the daylight period, an estimate of loss rates due to predation, indicated that the AAP bacteria in the upper 50 m of the water column turned over at rates of 0.75-0.90 d-1. This corresponded well with the specific growth rate determined in dilution experiments where AAP bacteria grew at a rate 1.05 ± 0.09 d-1. An amendment of inorganic nitrogen to obtain N:P = 32 resulted in a more than 10 times increase in AAP abundance over 6 days. The presented data document that AAP bacteria are an active part of the bacterioplankton community in the oligotrophic North Pacific Subtropical Gyre and that their growth was mostly controlled by nitrogen availability and grazing pressure.IMPORTANCEMarine bacteria represent a complex assembly of species with different physiology, metabolism, and substrate preferences. We focus on a specific functional group of marine bacteria called aerobic anoxygenic phototrophs. These photoheterotrophic organisms require organic carbon substrates for growth, but they can also supplement their metabolic needs with light energy captured by bacteriochlorophyll. These bacteria have been intensively studied in coastal regions, but rather less is known about their distribution, growth, and mortality in the oligotrophic open ocean. Therefore, we conducted a suite of measurements in the North Pacific Subtropical Gyre to determine the distribution of these organisms in the water column and their growth and mortality rates. A nutrient amendment experiment showed that aerobic anoxygenic phototrophs were limited by inorganic nitrogen. Despite this, they grew more rapidly than average heterotrophic bacteria, but their growth was balanced by intense grazing pressure.

Novel Alphaproteobacteria transcribe genes for nitric oxide transformation at high levels in a marine oxygen-deficient zone.

Marine oxygen-deficient zones (ODZs) are portions of the ocean where intense nitrogen loss occurs primarily via denitrification and anammox. Despite many decades of study, the identity of the microbes that catalyze nitrogen loss in ODZs is still being elucidated. Intriguingly, high transcription of genes in the same family as the nitric oxide dismutase (nod) gene from Methylomirabilota has been reported in the anoxic core of ODZs. Here, we show that the most abundantly transcribed nod genes in the Eastern Tropical North Pacific ODZ belong to a new order (UBA11136) of Alphaproteobacteria, rather than Methylomirabilota as previously assumed. Gammaproteobacteria and Planctomycetia also transcribe nod, but at lower relative abundance than UBA11136 in the upper ODZ. The nod-transcribing Alphaproteobacteria likely use formaldehyde and formate as a source of electrons for aerobic respiration, with additional electrons possibly from sulfide oxidation. They also transcribe multiheme cytochrome (here named ptd) genes for a putative porin-cytochrome protein complex of unknown function, potentially involved in extracellular electron transfer. Molecular oxygen for aerobic respiration may originate from nitric oxide dismutation via cryptic oxygen cycling. Our results implicate Alphaproteobacteria order UBA11136 as a significant player in marine nitrogen loss and highlight their potential in one-carbon, nitrogen, and sulfur metabolism in ODZs.IMPORTANCEIn marine oxygen-deficient zones (ODZs), microbes transform bioavailable nitrogen to gaseous nitrogen, with nitric oxide as a key intermediate. The Eastern Tropical North Pacific contains the world's largest ODZ, but the identity of the microbes transforming nitric oxide remains unknown. Here, we show that highly transcribed nitric oxide dismutase (nod) genes belong to Alphaproteobacteria of the novel order UBA11136, which lacks cultivated isolates. These Alphaproteobacteria show evidence for aerobic respiration, using oxygen potentially sourced from nitric oxide dismutase, and possess a novel porin-cytochrome protein complex with unknown function. Gammaproteobacteria and Planctomycetia transcribe nod at lower levels. Our results pinpoint the microbes mediating a key step in marine nitrogen loss and reveal an unexpected predicted metabolism for marine Alphaproteobacteria.

Sphingomicrobium clamense sp. nov., Isolated from Sediment of Clam Island Beach in China.

A Gram-stain-negative, non-flagellated, aerobic, ovoid or rod-shaped bacterium with motility, designated B8T, was isolated from the sediment of Clam Island beach, Liaoning province, China. The optimum growth of strain B8T occurred at 35 oC, pH 7.0, and in the presence of 4.0-5.0% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B8T formed a distinct lineage within the genus Sphingomicrobium and was closely related to Sphingomicrobium nitratireducens O-35T (98.3% sequence similarity), Sphingomicrobium aestuariivivum KCTC 42286T (96.9%), and Sphingomicrobium astaxanthinifaciens JCM 18551T (96.5%). The digital DNA-DNA hybridization and average nucleotide identity values between strain B8T and closely related strains were lower than 21.0% and 78.0%, much lower than the cutoff values of 70.0% and 95.0%, respectively, for bacterial species delineation. The dominant respiratory quinone of strain B8T was ubiquinone-10. The major fatty acids were Sum In Feature 8 (C18:1ω7c and/or C18:1ω6c), Sum In Feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), C17:1ω6c, C18:1 2-OH, and C16:0. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid, glycolipids, and four unknown polar lipids. The DNA G + C content of strain B8T was 63.9%. Based on the phenotypic, phylogenetic, and chemotaxonomic analyses, strain B8T is considered a new species of Sphingomicrobium, for which the name Sphingomicrobium clamense sp. nov. is proposed. The type strain is B8T (= CGMCC 1.19486T = KCTC 92052T).

Functionalization of seawater reverse osmosis membrane with quorum sensing inhibitor to regulate microbial community and mitigate membrane biofouling.

Membrane biofouling is a challenge to be solved for the stable operation of the seawater reverse osmosis (SWRO) membrane. This study explored the regulation mechanism of quorum sensing (QS) inhibition on microbial community composition and population-level behaviors in seawater desalination membrane biofouling. A novel antibiofouling SWRO membrane (MA_m) by incorporating one of quorum sensing inhibitors (QSIs), methyl anthranilate (MA) was prepared. It exhibited enhanced anti-biofouling performance than the exogenous addition of QSIs, showing long-term stability and alleviating 22 % decrease in membrane flux compared with the virgin membrane. The results observed that dominant bacteria Epsilon- and Gamma-proteobacteria (Shewanella, Olleya, Colwellia, and Arcobacter), which are significantly related to (P ≤ 0.01) the metabolic products (i.e., polysaccharides, proteins and eDNA), are reduced by over 80 % on the MA_m membrane. Additionally, the introduction of MA has a more significant impact on the QS signal-sensing pathway through binding to the active site of the transmembrane sensor receptor. It effectively reduces the abundance of genes encoding QS and extracellular polymeric substance (EPS) (exopolysaccharides (i.e., galE and nagB) and amino acids (i.e., ilvE, metH, phhA, and serB)) by up to 50 % and 30 %, respectively, resulting in a reduction of EPS by more than 50 %, thereby limiting the biofilm formation on the QSI-modified membrane. This study provides novel insights into the potential of QSIs to control consortial biofilm formation in practical SWRO applications.

Insight into planktonic protistan and fungal communities across the nutrient-depleted environment of the South Pacific Subtropical Gyre.

Ocean microorganisms constitute ~70% of the marine biomass, contribute to ~50% of the Earth's primary production, and play a vital role in global biogeochemical cycles. The marine heterotrophic and mixotrophic protistan and fungal communities have often been overlooked mainly due to limitations in morphological species identification. Despite the accumulation of studies on biogeographic patterns observed in microbial communities, our understanding of the abundance and distribution patterns within the microbial community of the largest subtropical gyre, the South Pacific Gyre (SPG), remains incomplete. Here, we investigated the diversity and vertical composition of protistan and fungal communities in the water column of the ultra-oligotrophic SPG. Our results showed apparent differences in protistan community diversity in the photic and aphotic regions. The entire protistan community diversity was significantly affected by temperature, salinity, oxygen, and nutrient concentrations, while the parasitic community diversity was also affected by chlorophyll a concentration. The parasitic protists were assigned to the class Syndiniales accounting for over 98% of the total parasitic protists, exhibiting higher relative sequence abundance along the water depth and displaying consistent patterns among different sampling stations. In contrast to the protistan community, the fungal community along the SPG primarily clustered based on the sampling station and pelagic zones. In particular, our study reveals a significant presence of parasitic protists and functionally diverse fungi in SPG and their potential impact on carbon cycling in the gyre.IMPORTANCEOur findings carry important implications for understanding the distribution patterns of the previously unrecognized occurrence of parasitic protists and functionally diverse fungi in the nutrient-limited South Pacific Gyre. In particular, our study reveals a significant presence of parasitic Syndiniales, predominantly abundant in the upper 300 m of the aphotic zone in the gyre, and a distinct presence of fungal communities in the aphotic zone at the central part of the gyre. These findings strongly suggest that these communities play a substantial role in yet insufficiently described microbial food web. Moreover, our research enhances our understanding of their contribution to the dynamics of the food webs in oligotrophic gyres and is valuable for projecting the ecological consequences of future climate warming.

Spatial and seasonal distribution of cyanobacteria Moorea species in coastal waters of Tanzania.

This study aimed at identifying the presence of harmful cyanobacteria, detecting potential harmful algae toxins and their distribution in three seasons: December to February (hot dry season), March to May (rainy season), and June to November (cool dry season) of 2016. The samples were collected in five study sites in Tanzania: Tumbe, Chwaka, Paje, Bweleo in Zanzibar islands and Songosongo Island, mainland Tanzania, where skin irritation problems were observed in seaweed workers in an earlier study. The cyanobacteria from the Moorea genus were microscopically detected in the seawater, with highest concentrations in the months with the highest seawater temperature or hot dry season, than in the other two seasons. The concentration of Moorea species was significantly higher in Songosongo, Tanzania mainland than in Zanzibar Islands in all three seasons, corresponding to the higher level of nutrients of nutrients (PO43-, NO3- and NH4+) in the prior season. However, the concentrations were considered relatively low and thus not collected during an ongoing algal bloom. This is one of the first studies that detect Moorea sp. in Tanzanian seawater, and complementary studies including genome sequencing to characterize the species are warranted.

Distinct bacterial succession and functional response to alginate in the South, Equatorial, and North Pacific Ocean.

The availability of alginate, an abundant macroalgal polysaccharide, induces compositional and functional responses among marine microbes, but these dynamics have not been characterized across the Pacific Ocean. We investigated alginate-induced compositional and functional shifts (e.g., heterotrophic production, glucose turnover, hydrolytic enzyme activities) of microbial communities in the South Subtropical, Equatorial, and Polar Frontal North Pacific in mesocosms. We observed that shifts in response to alginate were site-specific. In the South Subtropical Pacific, prokaryotic cell counts, glucose turnover, and peptidase activities changed the most with alginate addition, along with the enrichment of the widest range of particle-associated taxa (161 amplicon sequence variants; ASVs) belonging to Alteromonadaceae, Rhodobacteraceae, Phormidiaceae, and Pseudoalteromonadaceae. Some of these taxa were detected at other sites but only enriched in the South Pacific. In the Equatorial Pacific, glucose turnover and heterotrophic prokaryotic production increased most rapidly; a single Alteromonas taxon dominated (60% of the community) but remained low (<2%) elsewhere. In the North Pacific, the particle-associated community response to alginate was gradual, with a more limited range of alginate-enriched taxa (82 ASVs). Thus, alginate-related ecological and biogeochemical shifts depend on a combination of factors that include the ability to utilize alginate, environmental conditions, and microbial interactions.

Novel insights into the rhizosphere and seawater microbiome of Zostera marina in diverse mariculture zones.

BACKGROUND: Seagrasses offer various ecosystem services and possess high levels of primary productivity. However, the development of mariculture has affected the homeostasis of seagrass meadow ecosystems. Plant-microbiome associations are essential for seagrasses health, but little is known about the role of environmental microbiomes and how they affect seagrass in a mariculture environment. In this study, we investigated the influence of mariculture on the rhizosphere and seawater microbiome surrounding Zostera marina and focused on the bacterial, eukaryotic, and fungal components in the composition, diversity, metabolism, and responses to mariculture-related environmental factors. RESULTS: Significant differences in the composition, richness, diversity, and internal relations of the bacterial community between the seawater and rhizosphere sediment surrounding Z. marina were observed, while differences in the eukaryotic and fungal communities were less significant. More complex bacterial and fungal co-occurrence networks were found in the seawater and rhizosphere sediment of the Saccharina japonica (SJ) and sea cucumber (SC) culture zones. The seawater in the SJ zone had higher levels of dissimilatory and assimilatory nitrate reduction, denitrification, and nitrogen fixation processes than the other three zones. The assimilatory sulfate reduction enzymes were higher in the rhizosphere sediments of the SJ zone than in the other three zones. Tetracycline, sulfonamide, and diaminopyrimidine resistance genes were enriched in the mariculture SJ and SC zones. CONCLUSIONS: Our findings might contribute to a better understanding of the effects of mariculture on the seagrass and the meadow ecosystems and thus revealing their potential operating mechanisms. These insights may serve to raise awareness of the effects of human activities on natural ecosystems, regulation of antibiotic usage, and environmental restoration. Video Abstract.

Taxonomic and functional stability overrules seasonality in polar benthic microbiomes.

Coastal shelf sediments are hot spots of organic matter mineralization. They receive up to 50% of primary production, which, in higher latitudes, is strongly seasonal. Polar and temperate benthic bacterial communities, however, show a stable composition based on comparative 16S rRNA gene sequencing despite different microbial activity levels. Here, we aimed to resolve this contradiction by identifying seasonal changes at the functional level, in particular with respect to algal polysaccharide degradation genes, by combining metagenomics, metatranscriptomics, and glycan analysis in sandy surface sediments from Isfjorden, Svalbard. Gene expressions of diverse carbohydrate-active enzymes changed between winter and spring. For example, ß-1,3-glucosidases (e.g. GH30, GH17, GH16) degrading laminarin, an energy storage molecule of algae, were elevated in spring, while enzymes related to α-glucan degradation were expressed in both seasons with maxima in winter (e.g. GH63, GH13_18, and GH15). Also, the expression of GH23 involved in peptidoglycan degradation was prevalent, which is in line with recycling of bacterial biomass. Sugar extractions from bulk sediments were low in concentrations during winter but higher in spring samples, with glucose constituting the largest fraction of measured monosaccharides (84% ± 14%). In porewater, glycan concentrations were ~18-fold higher than in overlying seawater (1107 ± 484 vs. 62 ± 101 µg C l-1) and were depleted in glucose. Our data indicate that microbial communities in sandy sediments digest and transform labile parts of photosynthesis-derived particulate organic matter and likely release more stable, glucose-depleted residual glycans of unknown structures, quantities, and residence times into the ocean, thus modulating the glycan composition of marine coastal waters.

Possible transport pathway of diazotrophic Trichodesmium by Agulhas Leakage from the Indian into the Atlantic Ocean.

Diazotrophic cyanobacteria such as Trichodesmium play a crucial role in the nitrogen budget of the oceans due to their capability to bind atmospheric nitrogen. Little is known about their interoceanic transport pathways and their distribution in upwelling regions. Trichodesmium has been detected using a Video Plankton Recorder (VPR) mounted on a remotely operated towed vehicle (TRIAXUS) in the southern and northern Benguela Upwelling System (BUS) in austral autumn, Feb/Mar 2019. The TRIAXUS, equipped with a CTD as well as fluorescence and nitrogen sensors, was towed at a speed of 8 kn on two onshore-offshore transects undulating between 5 and 200 m over distances of 249 km and 372 km, respectively. Trichodesmium was not detected near the coast in areas of freshly upwelled waters but was found in higher abundances offshore on both transects, mainly in subsurface water layers down to 80 m depth with elevated salinities. These salinity lenses can be related to northward moving eddies that most probably have been detached from the warm and salty Agulhas Current. Testing for interaction and species-habitat associations of Trichodesmium colonies with salinity yielded significant results, indicating that Trichodesmium may be transported with Agulhas Rings from the Indian Ocean into the Atlantic Ocean.

The diversity of planktonic bacteria driven by environmental factors in different mariculture areas in the East China Sea.

Planktonic bacteria play a crucial role in sustaining the ecological balance of aquatic ecosystems. However, their seasonal variations in different aquaculture areas within the East China Sea, along with their correlation to environmental factors, have not been extensively explored. In this study, each area with 3 sample points were set up to represent the fish aquaculture area, shellfish aquaculture area and non-aquaculture area. In 2019, we undertook four marine surveys along the Xiasanhengshan uninhabited island, during which we gathered surface seawater samples for both physicochemical analysis and high-throughput sequencing. This allowed us to obtain data about the physicochemical properties and microbial composition in each surveyed region. A short-term eutrophication phenomenon was present in the sea, and the spatial and temporal distribution of planktonic bacteria differed based on the mariculture area. At the phylum level, Proteobacteria accounted for >50 % of the community abundance in winter, spring, and autumn, while Cyanobacteria accounted for >30 % of the community abundance in summer. Because Cyanobacteria blooms are likely in summer, the relationship between Cyanobacteria and environmental factors was studied. Redundancy analysis showed that Cyanobacteria were consistently positively correlated with phosphate. Eutrophication and abnormal proliferation of Cyanobacteria in the study area necessitate ameliorations in the mariculture structure. The variation of genus in Proteobacteria is consistent with that of eutrophication, so some genera in Proteobacteria have the potential to become biological indicator species.

Aggregating Synechococcus contributes to particle organic carbon export in coastal estuarine waters: Its lineage features and assembly processes.

The release and deposition of phytoplankton-derived particulate organic matter is crucial in marine carbon export, yet the roles of picoplankton in these processes were seldom considered. Therefore, this study aimed to shed light on the matter by investigating the aggregating (AG) lifestyle of Synechococcus, a main group of picoplankton, in the coastal waters of the Yellow River Estuary with ample sediments acting as ballast minerals. We revealed that AG Synechococcus constituted a substantial portion, maximally reaching up to 85.4 %, of the total Synechococcus population. Pearson correlations and random forest (RF) regression analyses found significant connections (p < 0.01) between AG Synechococcus and the content of particulate organic carbon (POC), which emphasized its underlying role in facilitating POC export in this region. Furthermore, by employing high-throughput sequencing of the RNA polymerase gene (rpoC1), it was demonstrated that S5.1 clade I exhibited a significantly higher proportion in the AG fraction than in the free-living (FL) fraction (p < 0.05). This suggests distinct inclinations in the phylogenetic preference for different Synechococcus lineages between different lifestyles in the studied area. Finally, we ascertained "small-world" and higher robustness attributes of aggregates formed through the co-occurrence construction between Synechococcus and heterotrophic bacteria, likely facilitated by the reciprocal exchange of carbon and nitrogen elements. Overall, these findings have implications for our understanding of the role of Synechococcus in the ecology and biogeochemistry of marine ecosystems, and they are significant for more accurately evaluating the contribution of picophytoplankton in ocean carbon export.

Disentangling microbial networks across pelagic zones in the tropical and subtropical global ocean.

Microbial interactions are vital in maintaining ocean ecosystem function, yet their dynamic nature and complexity remain largely unexplored. Here, we use association networks to investigate possible ecological interactions in the marine microbiome among archaea, bacteria, and picoeukaryotes throughout different depths and geographical regions of the tropical and subtropical global ocean. Our findings reveal that potential microbial interactions change with depth and geographical scale, exhibiting highly heterogeneous distributions. A few potential interactions were global, meaning they occurred across regions at the same depth, while 11-36% were regional within specific depths. The bathypelagic zone had the lowest proportion of global associations, and regional associations increased with depth. Moreover, we observed that most surface water associations do not persist in deeper ocean layers despite microbial vertical dispersal. Our work contributes to a deeper understanding of the tropical and subtropical global ocean interactome, which is essential for addressing the challenges posed by global change.

Depth-dependent microbial metagenomes sampled in the northeastern Indian Ocean.

The northeastern Indian Ocean exhibits distinct hydrographic characteristics influenced by various local and remote forces. Variations in these driving factors may alter the physiochemical properties of seawater, such as dissolved oxygen levels, and affect the diversity and function of microbial communities. How the microbial communities change across water depths spanning a dissolved oxygen gradient has not been well understood. Here we employed both 16S rDNA amplicon and metagenomic sequencing approaches to study the microbial communities collected from different water depths along the E87 transect in the northeastern Indian Ocean. Samples were collected from the surface, Deep Chlorophyll Maximum (DCM), Oxygen Minimum Zone (OMZ), and bathypelagic layers. Proteobacteria were prevalent throughout the water columns, while Thermoproteota were found to be abundant in the aphotic layers. A total of 675 non-redundant metagenome-assembled genomes (MAGs) were constructed, spanning 21 bacterial and 5 archaeal phyla. The community structure and genomic information provided by this dataset offer valuable resources for the analysis of microbial biogeography and metabolism in the northeastern Indian Ocean.